Dealing With Sedimentation Issues in Spate Irrigation Systems

Abstract

With growing water variability and scarcity in Africa a reality, a renewed interest in spate irrigation systems, which harness water in ephemeral environments, has emerged. Spate irrigation is seen as practical solution to supplement food production and improve food security in areas where water supply is scarce or highly variable. The political will in support of the system is evident in countries like Ethiopia, where significant investment is currently underway to upgrade the system. While the potential exists, the actual contribution of spate irrigation systems to food security has, so far, not been significant. One of the major reasons is the very high sedimentation rates of canals and irrigated fields. In spate irrigation systems sediment is a double‐edged sword. Fine sediment brings fertility and makes it possible to build up well‐structured soils, while on the other hand coarser sediment reduces spate flow diversion efficiency, raises the bed level and removes fields from the irrigation command. As is the case in several other countries, the spate irrigation systems in Ethiopia that were modernized through conventional civil engineering practices, lack effective technical and operational measures that maximize the benefits of sediments. To address this particular problem, a study was conducted in the Fokisa Spate Irrigation System in Ethiopia. The study employed field observations and simulations with various one‐dimensional hydraulic models. Primarily based on the study, but also drawing from experience in other spate irrigation systems, this paper analyses the effectiveness of settling basins and canal designs with non‐uniform cross sections and varying slopes. The results indicate that settling basins are not an optimal alternative and that designing canals with non‐uniform sections and slope leads to better performance. It is concluded that the former are not applicable in spate systems. Copyright © 2011 John Wiley & Sons, Ltd.

Sustainability of the Dujiangyan Irrigation System for over 2000 Years–A Numerical Investigation of the Water and Sediment Dynamic Diversions

“…A few examples are the spate irrigation system in Africa [31][32][33][34] and the ancient irrigation system in the Central Negev desert [35].…”

Mitigation of Sedimentation at the Diverstion Intake of Fota Spate Irrigation: Case Study of the Gash Spate Irrigation Scheme, Sudan

“…Sediment concentration measurement in Gash River started from 2004; however there was a lot of missing data and discontinuity in measurements. After 2008 the measurement of sediment concentration at Fota and Salamalikum station also interrupted [3]. For this study, measured silt and clay concentration is used.…”

“…Sedimentation is a real challenge for spate irrigation systems at the diversion structure from the river source. In almost all cases, flood water arrive with high sediment load, and creates serious problems at diversion intakes and canals network if it is not controlled and managed properly [3,4]. Therefore, the study of sedimentation is vital aspect for planning and design of a river basin.…”

Land use policy and agricultural water management of the previous half of century in Africa

“…From 2002 to 2007, pressurized irrigation was still growing (Kigalu et al 2008;Karlberg et al 2007;Kheira 2009b) and values of area waterlogged by irrigation and percentage of area equipped for irrigation salinized were decreased due to suitable management and decrease of agricultural water withdrawal. From 2007 to 2011, we could see a fall in agricultural water withdrawal (however, this index is allowable to increase if a suitable use), percentage of area equipped for irrigation salinized, and area waterlogged and a growth in spate irrigation that needs to specific attention to deal with sedimentation (Embaye et al 2012). The good event is raise of localized irrigation and its considerable impact on water conservation (Ward and Pulido-Velazquez 2008).…”